Land Acquisition and Ecosystem Carbon in California

Overview:

Protection of open space plays a key role in conservation of natural resources and provision of ecosystem services from natural ecosystems. The California State Coastal Conservancy (SCC) is authorized to facilitate land conservation across 30% of California (49,770 mi²), encompassing all or most of the counties bordering the coast and selected areas inland. Over 35 years, the SCC has undertaken more than 200 projects, protecting 550 parcels that cover almost a half million acres. Parcels vary in size, ecosystem type, land management practices (before and after acquisition) and alternative, highest value uses they may have been converted to if not protected. This diversity in geography and land use provides a unique opportunity to assess the impacts of land protection on ecosystem carbon sequestration due to avoided development and land management practices. Legislative mandates to reduce the carbon footprint of the state make such assessments increasingly important as part of conservation planning and project evaluation, and as a component of strategic planning for future SCC acquisitions.

Assessments of carbon sequestration broadly involve three distinct questions. The first is quantification of standing carbon stocks in any given vegetation type. Above-ground carbon is relatively easy to quantify, via remote-sensing and direct ground surveys. Below-ground carbon stocks, in contrast, require intensive soil sampling for direct measurement and spatial extrapolations that require more simplifying assumptions in the absence of remote sensing information.

The second question is how carbon stocks change over time, the balance of fluxes in and out of the ecosystem driving these changes, and the influence of land use, resource management, disturbance (especially fire), and vegetation change on these fluxes. Insight into these questions requires integration of observation and biogeochemical process models to estimate dynamics and interactions among multiple processes. Net increases in carbon stocks indicate positive carbon sequestration, and a contribution of ecosystem processes to mitigate rising greenhouse gas concentrations and consequent climate change.

The third component of carbon assessments is the evaluation of alternative scenarios for dynamics of carbon fluxes under contrasting management or land use, either in the past or future. Land acquisition has direct ecosystem benefits in terms of avoided development, but the ‘credit’ for these benefits depends on evaluations of what would have happened to the land had it not been acquired or protected. These evaluations are necessarily more challenging because they depend on counterfactual scenarios, and assessment of carbon consequences under counterfactual scenarios depends on model projections; direct validation of the projections is not possible except by comparison with other systems in space or time.

The project was completed in September 2017 and the report will be available later in the year.

Results of our project were presented in a webinar on Oct. 3, 2017. View the webinar here: